Peptidoglycan of Actinomyces naeslundii induces inflammatory cytokine production and stimulates osteoclastogenesis in alveolar bone resorption.

OBJECTIVE: Actinomyces naeslundii, plays an important role in forming dental biofilms and causes gingival inflammation. Although peptidoglycan, the major cell wall component of Gram-positive bacteria, has been demonstrated to induce inflammatory cytokines, little is known about the association of peptidoglycan with alveolar bone resorption. This study investigated the involvement of peptidoglycan from A. naeslundii in osteoclast formation and bone resorption.
DESIGN: Osteoclast formation and function induced by peptidoglycan of A. naeslundii T14V were examined using the co-culture system of MCTC3/PA6 cells and BALB/c mouse bone marrow cells. Osteoclast formation was evaluated to count TRAP-positive multi-nuclei cells as osteoclasts. The function of osteoclasts was assessed by measuring the areas of pits absorbed. Inflammatory cytokine genes expressions, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, were examined by RT-PCR analysis using murine peritoneal macrophages. Experimental periodontitis was performed in Sprague-Dawley rats orally infected with A. naeslundii.
RESULTS: TRAP-positive multi-nuclei cells and the areas of pits induced by peptidoglycan were significantly greater than controls (p<0.01). Gene expression levels of IL-1β, IL-6, and TNF-α induced by A. naeslundii PGN were stronger than controls. In experimental periodontitis, bone loss of A. naeslundii-infected rats was comparable to that of rats induced by Porphyromonas gingivalis, which has been reported to be a periodontal pathogenic agent, being significantly greater than that of the sham group (p<0.01).
CONCLUSIONS: These results suggest that peptidoglycan of A. naeslundii is an important virulence factor in the development of periodontitis.